Hydraulic circuit for effecting sequential operation of a plurality of positive displacement hydraulic motors of different sizes



Patented Aug. 3, 1948v HYDRAULIC CIRCUIT FOR EFFECTING SE- QUENTIAL OPERATION OF A PLURALITY OF POSITIVE DISPLACEMENT HYDRAULIC MOTORS OF DIFFERENT SIZES Benedict Weite, Lake Orion Township, Oakland County, Mich., asslgnor to Colonial Broach Company, Detroit, Mich., a'corporation o! Dela- Ware Original application July 23, 1943, Serial No.

495,856, now Patent No. 2,395,702, dated February 26, 1946.. Divided and this application September 25, 1944, Serial No. 555,617

2 Claims. (hCl. 60-52) The present invention relates to an improved hydraulic circuit for operating a machine incorporating a plurality of successively operated positive displacement hydraulic motors, and this application is a division of applicantsapplication, Serial No. 495,856, led July 23, 1943, now Patent No. 2,395,702, issued February 26, 1946. Theparticular embodiment of the invention illustrated is adapted for use in operating the cylinders of a pull-down broaching machine having a verticallymoving, broach-handling cylinder, a. verticallymoving, broach-pulling cylinder, and a horizontally-moving cylinder for shifting the Iwork into and out of breaching position. l

In prior hydraulic machines incorporating positive displacement pumps for operating a plurality of positive displacement motors at different times, it has been customary to design the pump to supply the maximum iiow required at any one time and to employ a safety by-pass relief valve to prevent the development of a destructive pressure in the system. As a result, when the flow requirements are low, the pump is operating against the maximum safe pressure for the system. This requires unnecessary power and results in'objectionable heating of the liquid.

Accordingly, it is the general objectv of vthe present, inventionl to provide in a machine of the type mentioned, means to limit the pressure on the system to a maximum value when the ilow requirements of the machine are high in combination with means operative when the iiow requirements of the machine are low to limit the pressure on the system to a lower value.

A more specic object of the invention is to provide, in combination with a by-pass valve for the outlet of the positive displacement pump, means operative in response to the development of a given pressure for opening the by-pass valve and thereby limiting the pressure to said given value, in combination with other means operative only when the flow requirements of `the machine are low to cause said valveto limit the pressure to a lower value.

Other objects and advantages of the invention will become apparent from the following specilil 2 ried by a stationary hollow piston rod 81. The piston rod 81 communicates with a manifold 3l,

and the manifold also supports a conduit 86 which projects into the cylinder 82 and communicates with the space above the piston. The machine also incorporates asimilarly constructed broachhandling cylinder Iitl containing a xed piston carried by a hollow piston rod |24. A second conduit |23 communicates with the lower end-of the cylinder I Ill, and the piston rod |24 and conduit |23 are xed to a manifold |25. It will be appreciated that the illustration of the above described structure is purely diagrammatic and that the two conduits leading to the opposite ends of the cylinder may be concentric, as pointed out in greater detail in the aforementioned copending application. The. machine also incorporates a positive displacement hydraulic motor |96, the movable piston rod of which is connected in any desired manner to the worktable of the machine.

The drawing is further simplied by illustrating the valve operating rods as dotted lines and by omitting most of the lines which run from the tank to the low pressure reservoir. are indicated by the letter T at their termination.

As shown in the drawing, the hydraulic system includesa tank or low pressure liquid reservoir 220 and a fixed displacement pump 22| having its inlet pipe 222 extending into the tank and its v discharge pipe 223 extending rto a speed and pressure control valve mechanism indicated generally at 224. The valve 224 has an internal cylindrical chamber 225 having a reduced end portion 226. The cylindrical chamber 225 contains a f piston 221 whichts the cylinder and carries at one side a valve plunger 228 which controls a port 229 leading, by means of pipe 230, to the tank. The opposite side of the piston carries a plunger 23| which fits the reduced bore 226 and a spring 232 normally acts upon the piston 221 to shift it in a direction to close port 229. The valve plunger 228 and the plunger 23| are of the same cation, the accompanying drawing, and the a'ppended claims.

The drawing illustrates diagrammatically one suitable embodiment of the invention particularly adapted for use in operating a hydraulic broaching machine of the type mentioned.

As shown in the drawings, the machine incorporates abroach pulling cylinder 82 adapted to move vertically with respect to a xed piston cardiameter, and the entire piston and plunger assembly is provided with a longitudinal opening from one end to the other, as best shown in dotted lines in the drawing. 1 'e The chamber -225 is in constant communication with the pump discharge line 223 and also with a passageway 233 which connects with an outlet pipe 234. The passageway 233 contains an adjustable throttle valve 235. The valve 235 is so constructed that itwill not entirely close the passageway 223 but may be adjusted tov provide a variable restriction tothe ow of liquid in the These lines i throttle valve 235.

passageway. The passageway 233 at a point beyond the throttle valve 235 is in constant communication with the right-hand end of the cylinder chamber 225 by means of a small bleed passageway 236 and a communicating passageway 231. The passageway 231, in turn, communicates through a ball check valve 2136 to the tank line 239.

The structure of the speed and pressure control valve so far described forms no part of the present invention. since it is conventional. The operation of the valve is as follows'.

Fluid from the pump, which may flow unrestricted through the line-223 and chamber 226 to the passageway 233, is subject to a restriction at the throttle valve 235 which causes a drop in pressure between that existing in the chamber 225 and that existing at the vdischarge end of passageway 233. Consequently, the .pressure at the discharge end of the passageway, which is communicated through passageway 236 and 231 to the right-hand end of the cylindrical chamber 225 and acts on the right-hand side of the piston 221, is lower than the pressure acting on the lefthand side of the piston 221. As a result, the difference in fluid pressure tends to force the piston to the right and open the port 229 to the tank, and

this tendency is resisted by the spring 232. The

spring 232 is relatively light and is constructed to permit opening of port 226 on a relatively small difference in pressure at the opposite sides of the piston, such as a difference in pressure in the order of eighteen pounds per square inch.

As a result of this arrangement, the piston 221 will shift to the right, thus opening port 229 at any time the pressure drop across the throttle valve 235 tends to exceed the pressure difference for which the spring 232 is set. 'I'his opening of port 226 by-passes a part of the constant flow of liquid from the pump to the tank and, consequently, reduces the flow across the throttle valve 235 and thereby reduces the pressure drop across the throttle valve until the pressure drop falls to or below that for which the spring 232 is set. Accordingly, the structure so far described functions to maintain automatically a flow through passageway 233 of sufficient fluid to cause a given pressure drop determined by spring 232 across the throttle valve, regardless ofthe pressure existing in the passageway 233. Since the only way in which the pressure drop across the valve 235 can be maintained uniform is by maintaining the quantity of liquid which flows past the valve uniform, the function of the valve mechanism so far described is to maintain a uniform rate of flow from passageway 233 to pipe `234, regardless of the resistance against which the pressure is flowing. The valve 235 is adjusted to pass `the quantity of liquid necessary to operate the broaching ram at the desired cutting speed; consequently, the ram will move at that speed, even though the resistance toits movement is variable.

It will be noted that in addition to operating as a speed control valve the valve 224 also performs the important function of insuring that the pressure against which the pump is discharging during the broaching and breach return strokes of the ram never exceeds the pressure required to move the breaching ram at the desired speed plus the small constant pressure drop across the This follows from the fact that the pressure in the pump discharge line 223 is always equal to the pressure in line 234 plus thel drop in pressure across the throttle valve 235, and the pressure in chamber 225 is automatically Vso maintained at a suiilcient level to pass the desired quantity of liquid through the valve 235 regardless of the resistance to ram movement. This is valve closed is set to open at the maximum allowable pressure, which may be in the order of a thousand pounds per square inch. If at any time the resistance is suiciently great to build up a pressure in pipe 234 and passageway 233 sufficient to open the check valve 236, the fluid in passageway 231 will immediately flow to tank through line 239 'and at a faster rate than it can be supplied through the small bleed passageway 236. As a result, the pressure in passageway 231 and, therefore, the pressure at the right-hand side of piston 221 will drop, allowing the pressure at the right-hand side of piston 221 to shift the piston to the right and open port 229, thus relieving the pressure on the system. l

It will be understood. that since the broach handling cylinder and the work table moving cylinder are much smaller than the broaching ram cylinder, they will require a smaller ow of liquid. Since valve 235 is set for the ow required to operate the ram cylinder, the valve 224 will not operate automatically as a speed or pressure cony trol valve during the movements of the handling cylinder and table cylinder.

However, means are provided for limiting the pressure developed by the pump during movements of the broach handling cylinder and the table cylinder. This means includes a port 242 in valve 224, which connects passageway 231 and a pressure control line 243 and means hereinafter described for controlling the pressure in line 243.

The uid from line 234 is conducted to a fourway valve, indicated generally at 250, which is provided with a spool having three lands 25|, 252 and 253, respectively. The valve housing is provided with a port 254 connected to the line 234, a port 255 connected to a discharge line v256, a port 251 connected to a discharge line 25B, and a pair of ports 260 at the ends of the housing which is connected by a passageway 26| to tank line 262. The valve is a pilot operated valve, being provided with a pair of pilot lines 264 and 265 leading to opposite ends of the valve. On admission of pressure to pilot line 264 and connection of line 265to the tank, the valve spool is shifted to the right into the position shown in the drawing, while it is shifted in the reverse direction if pilot pressure is applied to line 265 and line 264 is connected to the tank.

Pilot lines 264 and 265 are connected to ports 261 and 266 of a rotary four-way valve 266. The rotary valve 268 comprises one portion of a dual reversing valve, the other portion being indicated at 269. The two valves are connected by a shaft 216, indicated in dotted lines, to the reverse control handle 209, which may be mounted in any convenient location on the machine. The reversing valves 268 and 263 are illustrated in their forward or normal position, at which time port 266 communicates with'port 21| and port 261 communicates with port 212. Port 21| is conmeans of a line 214, and port 212 of valve 260 is connected to a port 216 of valve 201 by meansof a line 218.

As previously indicated, the valve 201 is a fourway valve controlled by trip dogs 200 and 20| connected to the piston of a movable worklxture, piston and cylinder` unit |96. The spool and ports of valve 201 are generally similar to those of valve 260 except that the spool 218 is provided with an enlargedv end portion 219 having a pair of spaced notches 290 and 28| adapted to co-operate with a spring-pressed detent 262, which acts to hold the spool against accidental displacement from either of its two positions of adjustment. When the spool is in the position shown in the drawing which it occupiesv when the piston is at the lower end of cylinder and piston unit |96 and the work fixture is in its loading position, pressure is transmitted from line 204, which is connected' to the pump discharge pipe 223 through line 286 to port 286, which is in communication with port 215. At the same time the tank line 281, which is connected to port 288, is in communication with port 213 and line 214. Pilot pressure is thus transmitted through valve 201 to line 216 and thence through valve 268 from port 212 to port 261 to pilot line 264 to the left-hand end ofthe main four-way control valve 250. At the same time, the right-hand pilot line 266 of valve 260 is connected to the tank through ports 266 and`21| of valve 266. line 214, port 213 and port 288 of valve 201, and line 291. This serves to hold the spool of valve 250 in the right-hand position shown in the drawing.

When the work table is shifted to its broaching position, the spool 218 of valve 201 is shifted to its upper position, thus reversing the connections to lines 2 14 and 216. At that time the-pilot pressure ows from port 286 to port 213, through line 214, from port 21| to port 266 of valve 268, and thence to the pilot line 265 at the right-hand end of valve 260. At the same time, the pilot line 264 at the left-hand end is connected with the tan'k through valve 268,1lne 216, and by communicating ports 216 and 211, passageway 289,

and port 298 of valve 201.

As a result of this arrangement, it is apparent that the main four-way valve 260 is reversed at each end of the stroke of the work xture cylinder and piston unit |96. 1f at any time during the cycle of operation it is desired to reverse the machine, the dual valve 268 and 269 is shifted to its reverse position. This reverses the connections between lines 264 and 266, on one hand, and lines'214 and 216, on the other, and thus reverses the valve ,plug have cut-away corners at 302 and 303, with the result that when the valve is in itscentral or stop position iluld may iiow from port 304 and port 306 through the passageway 306 in the valve plug to port 301. When valve 269 is in the forward position, shown in the drawing,

and thence to pipe 256. Pipe 256 is connected to the position of the spool of valve 260 with respect to the position of spool 210 of valve 201.- In theA reverse position of the valve 268 port 212 is in fluid communication with port 266 through the space 292 in the valve stem formed in the rotatable plug 293 of valve 268, and. port 261 is in communication with port 21| through the opening 294 in the valveplug. In the position shown in the drawing, the communication between ports 261 and 212,is through the opening 296 in the valve plug, shown in dotted lines. When the reversing handle 209 is shifted to the stop position, indicated by S in the drawing, the lands 296 and 291 block ports 266'and 261, with the result 266. y

The valve 269, which forms part ofthe dual reversing valve, is identical in construction to valve 268 except that the lands 300 and 30|' on space at the lower end of that no iluid can iiow through the valve port 306 is blocked because of the fact that port 3 03 is plugged, whlleport 304 is connected to port 301 through passageway 306. When the valve is shifted to reverse position, ports 305 and 301 are connected through passageway 306 and port 304 is blocked.

All of the parts in the drawing are in the position they assume when the machine is automatically stopped at the end of a broaching cycle and isin condition to be started on a new cycle of operation of the starting vhandle |34.

In the stop position illustrated, the valves are in 'such a position that fluid from' pipe v234 may dow through valve 250 from port 254 to portl 256 a check valve 8I0, which is so arranged as to permit relatively free flow from pipe 256 to a 4 pipe 261', but no return flow. Pipe 256 is also connected to a valve 3l l. Valve 3H is provided with a pair of ports 3|2 'and 3|3. Port 3|2 is connected to pipe 266, while port 3 i3 is connected to pipe 3|4 which', in turn, is joined by previously mentioned pipe 251'.- The spool 3|5 of valve 3| is normally unged by spring 3|6 into the position shown in the drawing, in which the land 3|1 of the spool blocks communication between ports 3|2 and 3I3. However, when pilot pressure is applied to the pilot line 3|8, which is connected to the lower end of the valve, the spool will be lifted, permitting communication between the ports 3|2 and 3|3. During the upward movement of the valve spool the iluid trapped above the land 3|1 is discharged through a small passageway 3|9 to the port 3|2. From pipe 3|4 the fluid may ilow through a short branch line 320 to a pilot operated valve 32|', which, in turn, is connected to a pipe 322. Valve 32| operates to block the flow of fluid from pipe 320 to pipe 322 except when pilot pressure is applied to the pilot line 323 leading to the upper end of the valve.

Valve 32| may be of any desired construction for example, it may be identical in lconstruction to valve 260 except that the ports corresponding to ports 265 and 260 are blocked and the pipes 320 andv322 are connectedto the ports which correspond to the ports 264 and 251 of valve 250.

Pipe 322 connects to a foot valve 324, which functions to permit relatively free iiow from line 322 to line 325 but offers suillcient resistance to return flow from line 325 to 322 to prevent the iluid trapped in the upper end of the cylinder ||0 from discharging through the piston rod |24 and pipe 325 under the influence of gravity acting on the cylinder and breach handling slide. The interior of valve 324 contains a cylindrical housing 326 provided with a pair of ports 321 and 323 and a spool 329 provided with a land 330 which, when the spool is held in its lower position illustrated by spring 33|, blocks communication between ports 321 and 328. Port 321 is connected by means of a passageway 332 to the the valve spool 329. Consequently. when the pressure in line 325, which is connected to port 321, reaches an amount suiii'cient to overcome the iniluence of spring 33|, spool 329 will lift, allowing flow from port 321 to port 328 andthence through passageway 333 to line 322. The tension of spring 33| is adjusted so that it will not open until the pressurein pipe 328 exceeds the pressure which is induced by the slide. Port 321 is also connected by passageway 334 to a channel 335 of a spring-pressed check valve 336 w-hich normally blocks a port 331 connected to passageway 333. The check valve 338 will permit relatively free flow from line 322,

through passageways 333 and 331 to channel 335 and through passageway 334 to port 321 and thence to pipe 325, When spool 329 is moved upwardly, the iluid trapped at the upper end is discharged to passageway 333 through passageway 338. Pipe 3|4 isv also in communication with the upper end of the breaching cylinder 82 through a foot valve 348, which is identical in construction te foot valve 324, and through pipe 34|.

Port 251 of valve 258 is in constant communication with the lower end of the breach handling cylinder ||8 through`plpe 258. branch pipe 343, and pipe |23. Pipe 258 may also be connected through valve 344 and pipe 345 te the lower end of the breaching cylinder 82 through piston red 81. Valve 344 is identical in construction and mode of operation to valve 32|, previously described, being controlled by pilot pressure in pilot lines 346 and 341.

The fluid for operating the work fixture cylinder and piston |96 is supplied through line 284 te valve 358, which forms one of the valves of the dual valve unit |11, the other valve being indicated at 35|. Valve 358 is identical in construction and mode of operation to valve 268, previously described, and hence need not be described in detail, while valve 35| is ef the same construction except that two of the ports are plugged.

In the drawing, the flow through valves 358 and 35| is indicated diagrammatically. Thus, in valve 358 the solid line 352 connecting ports 353 and 354 indicates that in the'position of the valve illustrated in the drawing ports 353 and 354 are in fluid communication with each other. At the same time, as similarly indicated, ports 355 and 356 are in communication. As a result of this, line 284 is connected through valve 358 to line |91, which leads to the upper end of the werk fixture cylinder and piston unit |96, while the line |98, which is connected to the lower end of the cylinder and piston unit |96, is connected through ports 355 and 356 of valve 358 to tank line 359. When valve 358 is shifted by clockwise rotation of the starting handle |34 to start the machine, port 353 is connected to port 356 and port 354' is connected to port 355, as indicated by the dotted lines in the drawing, thus supplying fluid pressure te the lower end of the piston and cylinder unit |96 and connecting the upper end to the tank. This immediately starts movement of the work nxture from its loading te its breaching position. The pilot line 3|8 of valve 3| l is connected te line |98 and hence pilot pressure is applied to valve 3|1| when the starting valve is shifted to starting position. y

When the machine is in the stop pesitioriillustrated, valve 35| connects a line 36| with a line 362, which, in turn, is connected to port 381 of valve 269 and thence through passageway 386 to port 384, from which it is connected by line 363 to the pressure control line 243. Consequently, when the valve 35| is shifted to its starting position, flow of fluid under pressure in line 362V is blocked, as indicated by the dotted lines on valve 35| in the drawing. The dual valve |11 is returned testarting position, as pre- 388 te port 38|.

viously indicated, at the end of the downward stroke of the breaching cylinder 82 by reason of the engagement of the trip dog |12 with the projection |1| on lever |68.

-The pilot pressure for controlling valve 32| 'is controlled by valve |88, which is also identical in construction to the valve i268, previously described. When the parts are in the stop position illustrated. the pressure line 284 is'cennected by a branch line 364 through valve |88 to the pilot line 323 leading to the upper end of valve 32|, while the pilot line 386 te the lower end of valve 32| is connected through valve |88 to the tank line 381 and, consequently, valve 32| is open. v

Valve |88 is operated by rod |33, which, in turn, is rotated by the arms |88 and |8| and trip dogs |82 and |83. When the breaching ram reaches the bottom of its downward stroke. trip deg |82 engages arm |8| and rotates shaft |33 and thus valve |88 to a position in which the pressure line 284 is connected to pilot line 388, as indicated in dotted lines on valve |88, and the tank line 361 is connected to pilot line 323, thus shifting the spool of valve 32| and blocking communication between pipes 328 and 322. When the breaching cylinder 82 reaches its uppermost position on its 'breach return stroke, trip deg |83 engages and rotates arm |88. thus returning valve |88 to the position shown in the drawing.

The pilot lines 346 and 341, which control valve 344, are controlled by valve 366, which is one of the valves of the dual valve |48, the other valve of the dual valve being indicated 388. Valve 368 is identical in construction to valve 268 and, in the position illustrated in the drawing, connects pilot line 346 through line 318 to the pressure line 284 and at the same time connects pilot line 341 to the tank line 31|. Under these circumstances, valve 344 is closed. When the Ibreach handling cylinder ||8 reaches the end of its downward stroke, trip dog |4'3 engages arm |39, thus rotating valve |48 counterclockwise until pilot line 341 is connected to line 318 and thence to the pressure line 284, while pilot line 346 is connected te the tank line 31|, as indicated in dotted'lines on valve 368. This shifts valve 344 and opens communication between pipes 258 and 345.

When the breach handling cylinder ||8 re- Vtu'rns te its top position, trip dog |42 engages arm |38 and returns dual valve |48 to the position shown in the drawing. The other valve 369 of dual valve |48 is also identical in construction to valve 268 except that ports 312 and 313 are plugged. In the s top position illustrated, valve 369 connects the tank line 314 to a line 315 which leads to port 316 et valve |6|. When the dual valve |48 is shifted at the bottom of the downward stroke of the breach handling cylinder ||8, communication between the tank line 314` and line 315 is blocked 'by valve 369.

Valve |6|, in the position shown in the drawing, provides a communication between port 316 'and port 311, the latter being connected to the aforementioned line 36|. It also provides communication between the pressure control line 243 and a line 319, this connection being from port Line 319 is connected to tank line 382 through a pressure relief valve 383, which is identical in contruction to the check valve 3|8 except that the spring which normally holds the check valve closed will not permit the valve to open until the pressure in line 319 ex- 'ceeds a predetermined pressure necessary to operate both the broach handling cylinder H8 and the work fixture cylinder and piston |96. The purpose of this valve is to prevent the pressure'in pressure control line 243, and, consequently, the -pressure discharged by the speed control valve 224 to line 234, from exceeding a predetermined pressure during the movements of the broach handling cylinder and the work ta'ble cylinder and piston unit |96 in view of the fact that these elements are not subject to the automatic speed and pressure control operation of valve 224. The pressure setting of valve 383, and, con sequently, the pressure delivered to pipe 234 during the movements of the broach handling cylinder ||0 and the work table is substantially less than the pressure required to operate the broaching cylinder 82.

Whenthe machine is stopped, it will be noted that the pressure control line 243 is connected through line 363, ports 3.04 and 381 of valve 269, line 382, valve 35|, line 36| through ports 311 and 316 of valve |6I, line 315, and valve 369 to the tank through tank line 314. Consequently, in the stop position. there is no pressure in line 243 and, therefore, valve plunger 228 will be fully opened and the pump will discharge through line 230 to the tank at a verylow pressure.

When the machine is shifted to starting position, valve 35| is shifted to disconnect line 362 from the tank. This enables the pressure to build up in line 243 andconsequently, during the operation of the work xture the pressure supplied by the pump will be limited only by the setting of valve 383.

'If at any time while the machine is stopped the broaching cylinder 82 sinks down lby gravity, spring 385 in valve 6| will shift the spool of valve |6| to the right and thus block all ow through valve |6I. This not only disconnects the line 362 and, therefore, line 36|' from line 315, which is connected to tank when the machine is stopped, but it also disconnects line 2,43 from the pressure relief valve 383, thus enabling the pressure to build up in line 243. As soon as the pressure builds up inline 243, the valve 224 -will close and raise the pressure supplied to the upper' end of the broach cylinder 82, thereby returning it to its i upper position. This insures that the broaching cylinder will not sink downwardly by gravity while the machine is in its stop position and the pump is operating. It also insures that the cylinder will be returnedto starting position as soon as the pump is started after an idle period.

' 'I'he machine operates in the following manner. With the parts in the stop position shown in the drawing and the pump running, passageway 231 in the speed and pressure vcontrol valve 224 will be connected directly to tank by lines 243, 363,

valve 269, line 362, valve 35|, line 36|, valve |6|, line 315, valve 369, and tank line 314. Consequently, the pressure in chamber 225 at the lefthand side of the piston 221 will not exceed the low pressure required to collapse spring 232, and allA of the oil discharged by the pumpwill flow through port 229 to the tank through line 230 except-the very small amount which will flow through the bleed passageway 236.

It will be noted that if while the machine 1s in the stop position illustrated the broaching cylinder 82 sinks down by gravity,trip dog |56 will leave arm |55 and allow the spring l385 of valve y |81 to shift the valve spool to a position in which it blocks all iow through the valve.) This immediately disconnects line 243 from'the vtank and allows the speed and pressure control valve 224 to build up a high pressure in the discharge pipe 234.. Since, as previously indicated, in the stop position fuid under pressure in pipe 234 is in communication with upper ends of the broach handlingfcylinder ||0 and the broaching cylinder 82, the broaching cylinder will be returned to the top of its stroke. This arrangement, therefore, constitutes an automatic means for prelling the broaching cylinder so that it will be at the top'of its stroke when the machine starts. At the same time, this arrangement will automatically insure that the broach handling cylinder remains at the top of its stroke. Incidentally, it may be noted that the foot valves 32,4 and 34,8 normally serve to prevent either -of the cylinders ||8 and 82 from falling by gravity whenthe machine is in its stop position. Consequently, the preiill arrangement need only take care of sinking movements due to unavoidable leakage.

It being assumed that the workpieces are secured to the moving worktable by any suitable Work holding fixture, not shown, the machine is started by rotating lever |34 in a clockwise direction. This rotates the dual valve I 11 from the position in which the ow conditions are illustrated in solid lines in the drawing to the position in which the ow 'conditions are illustrated in dotted lines. One of the valves of the dual valve tank line 382. The setting of the pressure relief valve 383 is such that ,the discharge to the tank will occur at a pressure in excess of that required to operate thework handling cylinder and piston |86 and suiiicient to operate the broach handling cylinder Fluid w111 then new from une m throughthe`\ other valve 358 of the dual valve |11 in the dotted\\` line path to line |98, which is connected to the lower end of the work handling piston and cylinder unit I 9 6, thus causing the piston to move upwardly, as viewed in the drawing, and shift the work table into broaching position. During this movement the liquid in the upper end of the cylinder and piston unit |96 returns to tank through line |91, valve 358 and line 353.

When the broaching xture reaches broaching position, trip dog 200 on slide |9| shifts the spool 218 of valve 281, thus reversing the pilot connections to valve 250, in the manner previously described. When the spool of valve 25|) thus shifts to the left, fluid under pressure in line 234 is transmitted to pipe 258 and flows unrestricted through line 343 and outer piston rod |23 to the lower end of the broach handling cylinder ||'8', causing it to move downwardly. At the same time, the fluid in the upper end of the cylinder returns to tank through the inner piston rod |24, pipe 325, foot valve 324, which then opens to permit ow from port 321 to port or channel 328. and thence through valve 32|, pipes 320 and 3|4,

valve 3| I, pipe 256, and line 262. At this time the through valve |6| and the pressure relief valve 383. During this movement of the broach handling cylinder, therefore, valve 224 does not act as a speed control valve, but simply as a pressure relief valve, due to the fact that the flow required to operate the broach handling cylinder is not sufficient on passing throttle valve 235 to cause a pressure drop sumcient to overcome the effect of spring 232. However, the pressure in valve chamber 225 cannot exceed the pressure determined by the setting of relief valve 383 plus the pressure required to overcome the spring 232 and, consequently, valve plunger 228 opens to a degree suillcient to maintain the desired pressure in the chamber 225 and line 234.

When the broach handling cylinder ||8 reaches the lower end of its stroke, trip dog |43 engages arm |33 and shifts the dual valve |48. One portion of the dual valve, namely valve ,368, is thus shifted into a position in which communication from line 315 to the tank line 314 is blocked. This insures that the pressure control line 243 and the branch thereof which includes line 363, valve 263, line 362, valve 35|, line 36|,fvalve |61' and line 315 will not be connected to tank when the valve 35| is subsequently returned to the position shown in the drawing. The other valve 368 of the-dual valve |48 on such shift reverses the pilot connections to valve 344 and thus permits the fluid under pressure in pipe 258 to ilow to pipe 345 and thence to the lower end of the breaching cylinder 82 in order to start the downward or broaching stroke of that cylinder. As soon as the breaching cylinder leaves its upper position, valve |6| is shifted into blocking position, disconnecting line 243 from the pressure relief valve 383 and tank line 382. This immediately eliminates control of valve 224 by the pressure relief valve 383 and enables the valve 224 to act as an automatic speed control and pressure relief valve during the remainder of the breaching or downward stroke of cylinder 82. During the breaching stroke, the return flow from the upper end of the cylinder 82 occursy iapplied to the lower pilot line 366 of valve 32| and the valve spool assumes the position in which it blocks ilow between pipes 328 and 322. At the same time, trip dog |12 engages the cam projection |1| on lever |68, thus returning the starting handle |34 in a counterciockwse direction to its stop position and, therefore, returning the dual valve |11 to the position shown in ing returns the valve to the solid line flow conditions illustrated in which the pilot line 3|! from l2 t the valve 3|| is connected to the tank line 353 and, consequently, the valve 3|| blocks the return of fluid from the upper end of the cylinder' 82 and positively stops the broaching stroke at the point determined by the setting of the trip dog |82. This makes it possible to adjust the breaching stroke to suit the needs of any particular job. It will be understood, of course, that any adjustment of the position of trip dog |32 will be accompanied by corresponding adjustment of trip dog |12 since both must operate at the same time.

When the valve 358, which forms part of the dual valve |11, is thus returned to the position shown in the drawing, the fluid connections to to the piston and cylinder unit |86 for the work fixture are reversed and iiuid under pressure from line 284 iiows through valve 358 to line |31 to the upper end of the cylinder, causing the piston to move downwardly as viewed in the drawing and retract the work from breaching position. During the return movement of the table the only pressure control eifective is the hish pressure relief action of valve 224 made possible by ball check valve 238.

When the piston of cylinder and piston'unit |33 returns to the position shown in the drawing, it shifts the spool 218 of valve 201 into the position shown in the drawing in which it connects pilot pressure through valve 268 tothe left-hand pilot line 264 of valve 250, thus shifting valve 258 to the right to the position shown in the drawing and initiating the broach return stroke of the broaching cylinder 82 by reason of the fact that iiuid under pressure in line/234 then iiows through valve 250 to line 256 through check valve 3|0, line 251, line 3|4, foot valve 348, pipe 34| and the outer piston rod 86 to the upper end of the broaching cylinder 82. The fluid in the lower end of the cylinder 82 returns to the tank through the inner piston rod 81, pipe 345, valve 344, pipe 258 and valve 250 tot` the tank line 262.

When the breaching cylinder reaches its uppermost position shown' in the drawing, trip dog |83 engages and shifts arm |80 to the position shown, thus rotating valve, |88 until it assumes the position in which the flow is indicated by solid lines in the drawing. In that position, pilot pressure is applied to the upper end of valve 32| by pilot line 323, thus causing the valve 32| to open and permit fiow from pipe 328 to pipe 322 and thus through the foot valve 324 past the check valve 336 therein to lirie 325 and thence to the inner piston rod |24 of the work handling cylinder IIB. This starts the broach return stroke of the work handling cylinder, i8.

At the same time valve |83 is shifted, trip dog |56 returns arm |55 to the position shown in the drawing, thus rotating shaft |3| in a clockwise direction and returning the spool of valve |6| to the position shown in which it connects port 316 to port 311 and connects port 388 to port 33|. As a result of the shift of valve |6I, the pressure in line 243 during the broach return movement of the broach handling cylinder |I8 is controlled by a pressure relief valve 383, in the manner previously describedi When the broach Handling cylinder |||l reaches the upper end of its\broach return stroke, trip dog |42 engages and shifts arm |38 and thus dual valve |48 to the position shown in the drawing in which line 315 is connected to tank through can only be initiated by manual shift of the starting handle I 34. When the machine thus stops, line 315 is connected through valve i6i,rline 36|, valve' 35i, line 362, valve 269, line 363 to the pressure control line 243, thus causing the valve 224 to discharge to tank at negligible pressure.' The shift of valve 368, which forms part of the dual valve |48, restores the pilot lines to valve 344 to the condition in which that valve blocks uid flow from line 259 to line 345 and thus completes the return of all parts to the stop position illustrated.

The stop and reverse valve is a dual valve comprising two valves 268 and 269. The valve 268 serves, when the reversing handle 209 is shifted from the forward position indicated F to the reverseposition indicated R. in the drawing, to simply reverse the pilot connections to the main control valve 259 and, consequently, reverse the direction of operation of the broaching and broach handling cylinders with respect to the direction they normally operate for a given posi;- tion of the work table. The valve 269 performs no function when the dual valve 2GB-269 is shifted to reverse position, but it is employed to stop the machine when the handle 209 is shifted to the intermediate stop position indicated S. In that position,- the pressure control line 243 is connected through line 362 to the tank port 395 and, consequently, the valve 224 discharges to tank at low pressure. In the intermediate stop position, all ports of valve 269 are blocked and no function is performed by that valve.

Although only one form of the invention is shown and described herein, it will be appreciated that various modifications and alterations may be made in the machine without departing vfrom the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. In a hydraulic machine, a pair of hydraulically operated motors of diierent liquid ilow requirements, a constant displacement pump, a reservoir connected to the intake of said pump, means including a liquid passageway connecting the pump discharge to said motors for automatically operating them successively through a cycle of operations, said passageway having a restriction therein, a Iby-pass valve for returning to the reservoir a portion of the liquid delivered by the pump, said by-pass valve being connected to said passageway between the pump and said restriction and having a cylinder, a piston in the cylinder, a valve plunger connected to the piston for controlling the by-p'ass, said piston being subject at one side to the pressure in the passageway between the pump and the restriction acting in a direction to open the'valve, means including a conduit connecting the liquid at the opposite side of said piston with the passageway on the opposite side of the passageway v sure exceeds a predetermined maximum and the restriction for maintaining the piston and valve plunger in such a position that a constant pressure drop is maintained across said passageway restriction, said pressure drop being that induced by a owhof liquid suilicient to operate the motorrhaving-the largest liquid flow requirement at the desired speed, a small bleed restriction in said lconduit, a pair of pressure relief valves connected in parallel between the liquid in the valve cylinder at said opposite side of the piston and the reservoir, one of said presp other being set to open at a lower pressure, said relief valves and their connections being less restricted when the relief valves are open than said conduit restriction, and means to block flow through said other relief valve when the motor having the largest liquid lflow requirement is operating.

2. In a hydraulic machine, a pair of hydraulically operated motors .of different liquid flow requirements, a constant displacement pump, a reservoir connected to the intake ot said pump, means including a liquid passageway connecting the pump discharge to said motors for automatically operating them successively through a cycle of operations and bring the machine to a stop, said passageway having a restriction therein, a by-pass valve for returning to the reservoir a portion of the liquid delivered by the pump. said by-pass valve -being connected to said passageway between the pump and said restriction and having a cylinder, a piston in the cylinder, a valve plunger connected to the piston for controlling the by-pass, said piston being subject at one side to the pressure in the passageway between the pump and the restriction acting in a direction to open the valve, means including a conduit ,connecting the liquid at the opposite side of said piston with the passageway on the opposite side of the passageway restriction for maintaining the piston and valve plunger in such a position that a constant pressure drop is maintained across said passageway restriction, said` pressure drop being that induced 'by a ow of liquid sufficient to operate the motor having the largest liquid ilow requirement at the desired speed, a small bleed restriction in said conduit, a pair of pressure relief valves connected in parallel between the liquid in the valve cylinder at said opposite side of the piston and the reservoir, one of said pressure relief valves being set to open when the pressure exceeds a predetermined maximum and the other being set to open at a lower pressure, said relief valves and their connections being less restricted when the relief valves are open than said conduit restriction, means to block flow through said other relief valve when the motor having the largest liquid flow requirement is operating, a third liquid connection between said liquid at the opposite side of the piston and the reservoir, manually operable means to close said third connection to start the machine, and means for automatically opening said connection for free flow to the reservoir when the machine completes a cycle of operations. l

BENEDICI WELTE.

' assurantien:sy crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,102,865 Vickers Dec. 2l, 1937 2,265,800 Connor et al. Dec.- 9, 1941 2,287,559 yNye June 23, i942 2,307,544 Rdbinson Jan. 5, 1943 2,318,851 Grilth May 1l, 1943 2,363,186 Nye Nov. 21, 1944 

